Allan S. Deutsch, D.M.D., F.A.C.D.
Which Burs to Use for Endo?
Allan Deutsch

Allan Deutsch

Although completing a molar endo may take up to one hour, the time I actually spend drilling on the tooth is relatively short.  Out of that one hour I may only take five to eight minutes drilling with my high-speed burs.  However, like many other preliminary procedures those initial minutes are exceedingly important to setting up the final result.
    What do we want to accomplish when using our high-speed handpiece?
  1. We want to gain access to the pulp chamber (without perforating the chamber floor).
  2. This access will enable us to find all the canals (even the ones that are hiding!)
  3. We want to have straight line access so that we can use our Peeso or gates to its full extent without having it break.
  4. We want to reduce the occlusion somewhat to avoid post-operative biting trauma and inflammation.
    In golf, a good grip enables a good swing, which gives us a good game (we hope).  In endo, finding the chamber enables us to find the canals, which enables us to complete the root canal therapy.  To this end I use two burs.  These burs accomplish 95 percent of my drilling.
    The first is a high-speed carbide number 4 round bur.  With this bur, I outline the chamber occlusally and remove enough dentin until I am in the pulp chamber.  This bur can actually help you avoid perforations.  Figure 1 shows the critical measurements on the bur.  It turns out that the ceiling of the pulp chamber measured from an occlusal cusp corresponds to length L of the bur.  When you hold the bur up over an accurate x ray you can see that when the ball is placed on the chamber ceiling the end of the taper of the shaft corresponds to the cusp tip (see Figure 2).  I now for the first time have a measurement guide as to how far down I am to drill into the tooth with my #4 round bur.
    When I look at the diagnostic x ray, one of things that I am looking at is the occlusal gingival height of the pulp chamber.  If the chamber is calcified, and therefore very narrow, I know I will not feel a drop when my bur reaches the chamber.  I therefore drill down to the line on the bur where the taper and parallel parts of the shaft meet and stop when this line is level with the cusp tip.  I now know I am a little below the ceiling of the pulp chamber.  This has given me the depth and a very rough outline of the chamber, I must now refine this preparation.
    I refine the preparation with the use of a high-speed coarse barrel diamond (Figure 3).  I lean the diamond against the axial wall and go around the outline of the prep (Figure 4). 
Figure 3

FIGURE 3: a high-speed coarse barrel diamond used to refine the preparation.

Figure 4

FIGURE 4: smoothing the wall and allowing light into the chamber.

This smooths the wall and allows a great deal of light into the chamber.  I next rinse the pulp chamber with Sodium Hypochlorite.  I remove the irrigant with a high-speed endo suction tip.  I can now easily see whether I have removed the entire ceiling of the pulp chamber.  Now I first start looking for the canals.  I also use this barrel diamond later to reduce the occlusion to avoid post-op pain due to prolongation of inflammation due to a high bite.  The barrel diamond is also used to push back the mesio-palatal axial wall in maxillary molars.  Along this mesio-palatal line in about 40?60 percent of the cases there is an extra canal.  This canal is called the MB2 or mesiobuccal prime canal.  It is responsible for a lot of molar endo failures if it is missed and not cleaned out.
    Simplifying your armamentarium down to two burs will speed up and simplify your endodontics.  

May-June 2002
Figure 1

FIGURE 1: The ceiling of the pulp chamber measured from an occlusal cusp corresponds to length L of the bur.

Figure 2

FIGURE 2: The end of the taper of the shaft corresponds to the cusp tip.

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